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Physiology Flashcards

1
Q

Define “osmolarity”

A

The concentration of osmotically active particles in a solution

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2
Q

What is the unit of osmolarity in the body?

A

mOsmol/L

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3
Q

What 2 factors need to be known to calculate osmolarity?

A

Molar concn of the solution

Number of osmotically active particles present

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4
Q

Calculate the osmolarity of a 150mM solution of NaCl

A

Osmotically active particles = NaCl = 2
Molar concn = 150
Osmolarity = 150 x 2 = 300 mOsmol/L

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5
Q

What is the difference between osmolality and osmolarity?

A

Osmolality has units of osmol/kg water

Osmolarity has units of osmol/L

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6
Q

What is the osmolarity of body fluids?

A

300 mOsmol/L

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7
Q

Define “tonicity”

A

The effect a solution has on cell volume (ability of solute to cross cell membrane)

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8
Q

If a solution is isotonic, what does this mean?

A

Water ECF = Water ICF

Cell volume is unchanged - no net movement of water

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9
Q

If a solution is hypotonic, what does this mean?

A

Water ECF greater than Water ICF

Cell volume increases - water moves into the cell (CELL LYSIS)

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10
Q

If a solution if hypertonic, what does this mean?

A

Water ECF less than Water ICF

Cell volume decreases - water moves out of the cell (CELL SHRINKAGE)

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11
Q

The cell membrane is very permeable to urea and sucrose. True/False?

A

False

Permeable to urea, impermeable to sucrose

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12
Q

If you placed a cell in a urea solution, what would happen?

A

Cell would increase in volume + burst, thus urea solution is hypotonic

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13
Q

What are the 2 fluid compartments that make up total body water? State their proportions

A 
Intracellular fluid (2/3)
Extracellular fluid (1/3)
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14
Q

List the components of extracellular fluid (ECF)

A

Plasma (20%)
Interstitial fluid (80%)
Lymph
Transcellular fluid

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15
Q

How can body fluid compartments be measured?

A

Tracers - obtain distribution volume

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16
Q

Give examples of tracers used to measure body fluid compartments

A

Total body water: tritated water
ECF: inulin
Plasma: labelled albumin

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17
Q

TBW = ICF + ECF. Which tracers would enable you to calculate ICF?

A 
Tritated water (TBW)
Inulin (ECF)
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18
Q

Give the equation to measure volume (V) of an unknown volume of water using a dosage (D) of tracer and sample concentration (C) of tracer

A

Dilution principle

V = D/C

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19
Q

List some methods of fluid input

A

Fluid intake
Food intake
Metabolism

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20
Q

List some insensible (non-regulated) losses of fluid

A

Skin

Lungs

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21
Q

List some sensible (regulated) losses of fluid

A

Sweat
Faeces
Urine

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22
Q

Water imbalance manifests as change in body fluid osmolarity. True/False?

A

True

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23
Q

How is water balance maintained?

A

By increasing/decreasing fluid intake

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24
Q

Is the concn of Na higher in the ECF or ICF?

A

Na is higher in the ECF

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25
Is the concn of Cl higher in the ECF or ICF?
Cl is higher in the ECF
26
Is the concn of K higher in the ECF or ICF?
K is higher in the ICF
27
Is the concn of HCO3 higher in the ECF or ICF?
HCO3 is higher in the ECF
28
The osmotic concn of the ECF = the osmotic concn of the ICF. True/False?
True | 300 mosmol/l
29
What is meant by fluid shift in body compartments?
Movement of water between ECF and ICF in response to an osmotic gradient
30
What would happen to the ICF if the osmotic gradient of the ECF increased?
Osmotic gradient increase = lose water | Therefore, osmolarity increases, causing ECF to become hypertonic, so cell volume decreases i.e. ICF volume decreases
31
What would happen to the ICF if the osmotic gradient of the ECF decreased?
Osmotic gradient decrease = gain water | Therefore, osmolarity decreases, causing ECF to become hypotonic, so cell volume increases i.e. ICF volume increases
32
If you add salt to the ECF, what happens to the ICF?
ECF becomes hypertonic so ICF decreases
33
If you remove salt from the ECF, what happens to the ICF?
ECF becomes hypotonic so ICF increases
34
If you administer 0.9% NaCl solution IV, what happens to fluid osmolarity?
No change in osmolarity; change in ECF volume only
35
Which ion is chiefly responsible for the osmolarity of the ECF?
Na
36
Which ion is chiefly responsible for the osmolarity of the ICF?
K
37
Salt imbalance manifests as change in ECV. True/False?
True
38
List the main functions of the kidney
``` Water and salt balance Maintaining fluid volume and osmolarity Acid-base balance Excretion of waste Secretion of renin, erythropoietin Convert inactive vitamin D to calcitriol ```
39
What % of the cardiac output goes to kidneys?
20-25%
40
What 3 processes occur in a nephron?
Filtration Reabsorption Secretion
41
Describe the flow of arterial blood into the kidney involving its transformation into tubular fluid
Renal artery - afferent arteriole - glomerulus - 20% to Bowman's capsule, 80% to efferent arteriole - renal tubules - peritubular capillaries - renal vein
42
What are the 2 types of nephron?
Juxtaglomerular (20%) | Cortical (80%)
43
How do juxtaglomerular and cortical nephrons differ?
Juxtaglomerular: vasa recta instead of PT capillaries, long loop of Henle Cortical: PT capillaries, short loop of Henle
44
Which nephrons produce concentrated urine?
Juxtaglomerular nephrons
45
The diameter of the afferent arteriole is greater/smaller than the efferent arteriole
The diameter of the afferent arteriole is greater than the efferent arteriole
46
Which cells secrete renin in the juxtaglomerular apparatus?
Granular cells
47
What do the cells in the macula densa do?
Sense salt composition of distal convoluted tube fluid
48
How do you calculate the rate of filtration of substance X in the kidney?
X = mass of X filtered per unit time = [X]plasma x GFR
49
How do you calculate the rate of excretion of substance X in the kidney?
``` X = mass of X excreted per unit time = [X]urine x Vu (Vu = volume of urine) ```
50
How do you calculate the rate of reabsorption of substance X in the kidney?
Rate of reabsorption of X = rate of filtration of X - rate of excretion of X
51
How do you calculate the of secretion of substance X in the kidney?
Rate of secretion of X = rate of excretion of X - rate of filtration of X
52
If rate of filtration of X is greater than rate of excretion of X, has net reabsorption or secretion taken place?
Net reabsorption
53
If rate of filtration of X is less than rate of excretion of X, has net reabsorption or secretion taken place?
Net secretion
54
The endothelial pores in the glomerular capillary are 100x larger than the capillaries found elsewhere in the body. True/False?
True
55
What are the 3 main barriers to filtration in the glomerulus?
``` Glomerular capillary endothelium (barrier to RBC) Basement membrane (barrier to plasma protein) Slit processes of podocytes (barrier to plasma protein) ```
56
Name the 4 main forces that comprise net filtration pressure
BPgc - Blood pressure of capillary HPbc - Hydrostatic pressure of Bowman's capsule COPgc - Oncotic pressure of capillary COPbc - Oncotic pressure of Bowman's capsule
57
Glomerular filtration is a passive process. True/False?
True
58
Describe the effect of BPgc (blood pressure of glomerular capillary)
High (55 mm Hg) pressure constant across the capillary that favours filtration
59
Describe the effect of HPbc (hydrostatic pressure of Bowman's capsule)
Fluid in the Bowman's capsule opposing filtration (15 mm Hg)
60
Describe the effect of COPgc (oncotic pressure of glomerular capillary)
Opposes filtration of plasma proteins due to concn gradient (30 mm Hg)
61
Describe the effect of COPbc (oncotic pressure of Bowman's capsule)
Negligible since there are no plasma proteins in Bowman's capsule (0 mm Hg)
62
What is the rough normal value of net filtration pressure?
10 mm Hg favouring filtration
63
What is glomerular filtration rate (GFR)? Give the equation for calculating this
Rate of filtration of protein-free plasma is filtered from the glomeruli into the Bowman's capsule per unit time. ``` GFR = Kf x net filtration pressure Kf = filtration coefficient (how holey the glomerular membrane is) ```
64
What is the normal GFR value?
125 ml/min
65
Which pressure is the major determinant of GFR?
Glomerular capillary blood pressure (BPgc)
66
A decreased GFR results in decreased urine volume. True/False?
True
67
How is GFR controlled extrinsically?
Sympathetic control via baroreceptor reflex
68
How is GFR controlled intrinsically?
``` Myogenic mechanism (vascular SM stretch in increased ABP causes vasoconstriction) Tubuloglomerular feedback mechanism (GFR increase causes increased NaCl through tubule, resulting in afferent arteriole constriction) ```
69
If arterial blood pressure increases, what happens to GFR and net filtration pressure?
GFR and NFP increase with increasing arterial BP as there is increased blood flow to glomerulus afferent arteriole
70
If vasoconstriction of the afferent arteriole occurs, what happens to GFR and net filtration pressure?
GFR and NCP decrease with vasoconstriction
71
How does decreased urine volume arise from a fall in blood volume?
Fall in BP causes fall in arterial blood pressure which is detected by baroreceptors that fire to activate sympathetic nervous system; this causes arteriolar vasoconstriction to decrease BPgc and thus decrease GFR, causing decreased urine volume
72
Changes in arterial blood pressure always result in changes in GFR. True/False?
False Autoregulation prevents short-term changes in arterial blood pressure affecting GFR i.e. intrinsic control
73
What is the equation for calculating mean arterial blood pressure?
(1/3 x [systolic - diastolic]) + diastolic
74
How do the macula densa cells contribute to intrinsic control of GFR?
Sense salt in distal tubule and release vasoconstrictive mediators (in response to salt) in a -ve feedback loop, causing decreased GFR TUBULOGLOMERULAR FEEDBACK
75
What effect does a kidney stone have on GFR?
Kidney stone causes increased HPbc, causing decreased GFR
76
What effect does diarrhoea have on GFR?
Diarrhoea causes increased COPgc, causing decreased GFR
77
What effect does severe burns have on GFR?
Severe burns causes decreased COPgc, causing increased GFR
78
What is plasma clearance?
A measure of how effectively the kidneys can clear a substance from blood = volume of plasma containing a substance cleared per minute (ml/min)
79
Give the equation for plasma clearance of substance X
([X]urine x Vu) / [X]plasma
80
Which substance has a plasma clearance equivalent to GFR?
Inulin - it is neither absorbed or secreted, so can be used as a measure of GFR
81
Why is creatinine not as good as inulin as a measure of GFR?
Creatinine undergoes small amount of secretion so not quite as accurate but easier to measure clinically
82
Glucose is normally completely reabsorbed and not secreted. True/False?
True | Should have 0 clearance
83
Give an example of a substance that is partly reabsorbed and not secreted
Urea | About 50% is reabsorbed
84
The clearance of urea will be less/greater than the GFR
The clearance of urea will be less than the GFR
85
Give an example of a substance that is secreted but not reabsorbed
H+
86
The clearance of H+ will be less/greater than the GFR
The clearance of H+ will be greater than the GFR
87
If clearance is less than the GFR, the substance is reabsorbed/secreted/neither reabsorbed or secreted
If clearance is less than the GFR, the substance is reabsorbed
88
If clearance is equal to the GFR, the substance is reabsorbed/secreted/neither reabsorbed or secreted
If clearance is equal to the GFR, the substance is neither reabsorbed or secreted
89
If clearance is greater than the GFR, the substance is reabsorbed/secreted/neither reabsorbed or secreted
If clearance is greater than the GFR, the substance is secreted
90
Which substance helps us calculate renal plasma flow? What is a normal renal plasma flow?
Para-amino hippuric acid (PAH) | 650 ml/min
91
Why is PAH useful for measuring renal plasma flow?
Freely filtered at glomerulus Secreted into tubule (not reabsorbed) Completely cleared from plasma i.e. all PAH in plasma that escapes filtration is secreted from peritubular capillaries anyway
92
A marker of renal blood flow should be filtered and completely secreted. True/False?
True
93
What is filtration fraction? | Give the equation for calculating filtration fraction
Fraction of plasma that is filtered by the glomerulus | GFR/renal plasma flow (usually 20%)
94
Where does most reabsorption of substances occur in the nephron?
Occurs along whole length, but most occurs in proximal tubule
95
List substances reabsorbed in the proximal tubule
``` Sugar Amino acid Phosphate Sulphate Lactate ```
96
List substances secreted in the proximal tubule
``` H+ Hippurates (PAH) Neurotransmitter Bile Uric acid Drugs Toxin ```
97
Where is the Na-K pump always found?
Basolateral membrane
98
Describe the movement of Na and K across the Na-K pump
2 K in, 3 Na out of cell against concn gradient
99
Is the Na-glucose transporter an example of cotransport or antiport?
Co-transport
100
Is the Na-H transporter an example of cotransport or antiport?
Antiport
101
How does water couple its reabsorption with ion transport?
Movement of Na towards blood creates electrochemical gradient for Cl movement which follows Na; this creates an osmotic gradient for movement of water (Water follows sodium)
102
When does reabsorption of glucose stop?
When renal threshold is reached and cotransporters are fully saturated
103
Tubular fluid is iso-osmotic when it leaves the proximal tubule. What does this mean?
Osmolarity = 300 mOsmol/L
104
What is the function of the Loop of Henle?
Generate cortico-medullary concn gradient to enable production of hypertonic urine
105
What is the term for opposing fluid flow in the two limbs of the Loop of Henle? What is the function of this?
Countercurrent multiplication | Kidney can produce urine of different volumes depending on ADH content
106
Which ions are reabsorbed in the ascending loop of Henle?
Na, Cl | Thick = active transport, thin = passive transport
107
Little or no water reabsorption occurs in the ascending loop of Henle. True/False?
True
108
The descending loop of Henle reabsorbs a lot of salt. True/False?
False | Mainly water reabsorption
109
The triple cotransporter enables reabsorption of which ions? Which drug class inhibits this cotransporter? Where in the nephron is this located?
Na, Cl, K Loop diuretics block the cotransporter Thick (upper) ascending loop of Loop of Henle
110
How does salt pumped out of ascending limb affect the osmolarity of the interstitial fluid?
Osmolarity of interstitial fluid increases
111
The distal tubule is not permeable to urea. True/False?
True
112
Hormones (ADH, aldosterone) only influence permeability of distal tubule and collecting duct. True/False?
True
113
ADH causes water excretion. True/False?
False | ADH causes water reabsorption
114
What is the effect aldosterone upon K, H and Na?
Increases Na reabsorption | Increased K and H secretion
115
What is the effect of ANP on Na? Why?
Decrease Na reabsorption due to stretch of atrial muscle cells
116
Is distal tubular fluid hypo, hyper or iso osmotic?
Hypo-osmotic
117
What ion transport occurs in the early and late distal tubule respectively?
Na-K-2Cl cotransport Reabsorption: Ca, Na, K Secretion: H+ Secretion: K+ due to aldosterone
118
What ion transport occurs in the early and late collecting duct respectively
Similar to late distal tubule Low ion permeability High water and urea permeability
119
Where are the aquaporin/vasopressin type 2 receptors (sensitive to ADH) located?
Apical membrane
120
High ADH causes hypotonic urine. True/False?
False | High ADH causes water reabsorption by inserting new aquaporin channels, so urine will be hypertonic
121
Decreased atrial pressure causes increased/decreased ADH release
Decreased atrial pressure causes increased ADH release
122
What is the effect of nicotine and alcohol on ADH?
Nicotine stimulates ADH release | Alcohol inhibits ADH release
123
What is the effect of aldosterone on Na and K? Why?
Aldosterone promotes Na reabsorption and K release | Increase Na K pumps at basolateral membrane
124
What 3 mechanisms increase renin release in the juxtaglomerular apparatus?
Reduced BP in afferent arteriole Macula densa cells sense decreased salt in DT Increased sympathetic stimulation
125
What is the equation for calculating pH?
pH = 1/log[H]
126
The pH of arterial blood is more alkali than the pH of venous blood. True/False?
True pH of arterial blood = 7.45 pH of venous blood = 7.35
127
What is the average pH of blood?
7.4
128
Small changes in pH reflect small changes in [H+]. True/False?
False | Large changes in [H+] cause small changes in pH
129
What is the effect of increasing [H+] on pH?
pH decreases with increasing [H+]
130
How do fluctuations in [H+} alter nerve/CNS activity?
Acidosis causes CNS depression | Alkalosis causes overexcitability of PNS and CNS
131
List the 3 sources of [H+] addition into the body
``` Carbonic acid formation Inorganic acids (from breakdown of nutrients) Organic acids (from metabolism) ```
132
What is the relationship between strong + weak acids and dissociation in solution?
Strong acids dissociate completely in solution | Weak acids dissociate partially in solution
133
HA --- H+ + A- | If acid [H+] is added, what happens to equilibrium?
Equilibrium shifts to left to produce more HA | A- ions mop up H+ ions to buffer any decrease in pH
134
HA --- H+ + A- | If base [A-] is added, what happens to equilibrium?
Equilibrium shifts to right to dissociate more HA | Rise in pH (caused by excess A-/fall in H+) is buffered by dissociation of HA
135
What is the equation for calculating equilibrium constant (K)?
K = [H][A]/[HA]
136
State the Henderson-Hasselbach equation
pH = pK + log[A]/[HA]
137
State the equation for calculating pK
pK = -logK = -log[H][A]/[HA]
138
The most important physiological buffer is the CO2-HCO3 buffer. What is the equilibrium equation?
CO2 + H20 (lungs) --- H2CO3 --- H+ + HCO3- (kidneys)
139
Which enzyme catalyses the formation of carbonic acid?
Carbonic anhydrase
140
What does control of [HCO3-] depend on?
H+ secretion into the tubule
141
How can the kidneys generate new HCO3- when buffer stores are low (i.e. when [HCO3-]tubular-fluid is low)?
H+ combines with phosphate buffer to cause net gain of HCO3-
142
What is meant by titratable acid?
The amount of H+ excreted via phosphate buffer in the kidney (when tubular HCO3 is low) Measure the amount of strong base added to the titrate to buffer the pH back to 7.4 i.e. to reverse addition of H+
143
What 3 things happen as a result of H+ tubular secretion?
Reabsorption of HCO3 (prevent acidosis) Formation of acid phosphate Formation of ammonium ion
144
What is the difference between compensation and correction of acid-base balance?
Compensation: restore pH regardless of HCO3 and CO2 levels Correction: restore pH, HCO3 and CO2 to normal
145
Respiratory acidosis is caused by ________. List some disease causes
CO2 retention COPD Chest injuries Respiratory depression
146
What is the compensatory mechanism for respiratory acidosis?
Drives equilibrium to right Renal system compensates due to respiratory cause Increase H+ secretion and generate titratable acid which forms new HCO3 i.e. ultimately increase HCO3 added to blood
147
Respiratoy alkalosis is caused by ______. List some disease causes
Excess CO2 removal Low inspired PO2 at altitude Hyperventilation
148
What is the compensatory mechanism for respiratory alkalosis?
Drives equilibrium to left Renal system compensates due to respiratory cause HCO3 excretion - no titratable acid is formed so no generation of new HCO3 i.e. ultimately decrease HCO3
149
Metabolic acidosis is caused by _______ from any source other than CO2. List some disease causes
Excess H+ Ingestion of acid foodstuff Metabolic production (lactic acid) Loss of base from body (diarrhoea)
150
What is the compensatory mechanism for metabolic acidosis?
Respiratory system compensates as it is not cause Hyperventilation - blow off CO2 i.e. ultimately lower H+
151
Metabolic alkalosis is caused by ________ from body. List some disease causes
Excess loss of H+ Vomiting (loss of HCl) Ingestion of alkali (antacid) Aldosterone hypersecretion
152
What is the compensatory mechanism for metabolic alkalosis?
Respiratory system compensates as it is not cause Slow ventilation - retain CO2 i.e. ultimately increase H+
153
What is the juxtaglomerular apparatus?
Distal tubular structure between afferent and efferent arterioles
154
List the components of the structure of a nephrone
``` Bowman's capsule Proximal convulated tubule Loop of Henle (ascending and descending loop) Distal convulated tubule Collecting duct Renal pelvis ```
155
What three factors minimise blood flow washing away NaCl and urea?
Vasa recta capillaries follow hairpin loops Vasa recta capillaries freely permeable to NaCl and H20 Blood flow to vasa recta is low
156
What is the function of the distal tubule and collecting duct?
Sites for regulation of ion and water balance
157
List stimulus for ADH release
Mostly hypothalamic osmoreceptors | Activation of left atrial stretch receptors in large changes of ABP
158
Outline the RAAS pathway when ABP is reduced
Angiotensin produced in liver --> Renin produced in kidney --> Angiotensin 1 to angiotensin 2 in lungs via ACE --> Arteriolar vasoconstriction and increased ADH --> Aldosterone produced in adrenal cortex --> Increased Na and Cl reabsorption in kidney Hold H20 in ECF Conserve H20
159
What is normal acid base balance?
1. Plasma pH = 7.35 -7.45 (7.4) 2. HCO3p = 23-27 (25) 3. Arterial pCO2 = 35 - 45 (40)

Y2 RENAL (17 decks)

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